Application of Fuzzy Control in ABR - CT Service in Presence of VBR Traffic and Performance Evaluation under Realistic Traffic Models

摘要

The Available Bit Rate (ABR) service has been proposed by the ATM Forum in 1994 and also adopted by the ITU shortly afterwards. The paper presents the performance of a credit based scheme, called Controlled Transfer (CT) algorithm, when the ABR traffic is statistically multiplexed with Variable Bit Rate (VBR) data streams. The performance evaluation has been carried out via simulation and considering realistic traffic models. The presence of VBR traffic severely deteriorates the performance of the ABR-CT algorithm and for that reason a fuzzy control mechanism is being proposed. The controller is taking into consideration the congestion degree of every switch and depending on its available resources attempts to reallocate them without violating the negotiated parameters of the connections. In addition, the controller does not operate in favor of any specific ABR connection, which is crucial for the ABR service requirements. Two different controller approaches are tested. The first is centralized, less scalable but performs slightly better while the second is distributed, very scalable, very flexible and its performance gives satisfactory results. Our conclusion is that the distributed approach should be employed because of its flexibility in implementation and its scalability with a large number of connections.